The human body has a number of internal body lumens, as in the gastrointestinal tract, with an inner lining or layer that can be susceptible to disease. As an example, gastroesophageal reflux disease (GERD), which involves inappropriate relaxation of the lower esophageal sphincter, manifests with symptoms of heartburn and regurgitation of gastric and intestinal contents. Patients with severe forms of gastroesophageal reflux disease can sometimes develop secondary damage of the esophagus due to the interaction of gastric or intestinal contents with esophageal cells not designed to experience such interaction.
The esophagus is composed of three primary tissue layers; a superficial mucosal layer lined by squamous epithelial cells, a middle submucosal layer and a deeper muscle layer. When gastroesophageal reflux occurs, the superfacial squamous epithelial cells are exposed to gastric acid, along with intestinal bile acids and enzymes. This exposure may be tolerated, but in some cases can lead to a condition known's as Barrett's esophagus, in which damage and alteration of the squamous cells causes them to change into taller, specialized columnar epithelial cells. Barrett's esophagus has important clinical consequences, as the columnar cells can become dysplastic, and then further progress to adenocarcinoma of the esophagus.
Accordingly, attention has been focused on identifying and removing this abnormal Barrett's columnar epithelium in order to mitigate more severe implications for the patient. Devices and methods for treating abnormal body tissue by application of various forms of energy to such tissue have been described, such as radio frequency ablation. However, precise control of the depth of penetration of the energy means, these methods and devices is critical to the success of such ablational therapy. Uncontrolled energy application can penetrate too deeply into the esophageal wall, beyond the mucosa and submucosal layers, into the muscularis externa, potentially causing esophageal perforation, stricture or bleeding. Among the factors and information needed for administration of the correct amount of treatment energy to the tissue is knowledge of the size of the esophagus and area to be treated.
Medical procedures for treating Barrett's esophagus typically involve deployment of an expandable catheter inside the esophagus. Expandable catheters are preferred because the profile of the catheter is ideally as small as possible to allow for ease of delivery, while treatment of the esophagus is most efficiently performed when the catheter is at or slightly larger than the diameter of the esophageal wall. Proper sizing and/or pressurization of the delivery device is desirable to prevent over-distension of the organ, which can result in harm to the organ, or under-expansion of the catheter, which can results in incomplete treatment. Accordingly, accurate and simple measurement of the size of the lumen and control of the pressure of the catheter on the lumen surface promotes the proper engagement and delivery of energy to the luminal wall so that a uniform and controlled depth of treatment can be administered.
Ablational devices typically need to make an appropriate and reproducible therapeutic contact between an ablational surface and the surface of a tissue area targeted for ablation. A number of ablational devices and methods for using them have been described in US patents and applications (U.S. Pat. No. 6,551,310 of Ganz issued on Apr. 22, 2003, application Ser. No. 10/370,645 of Ganz published as US2003/0158550 on Aug. 21, 2003, application Ser. No. 10/426,923 of Stern published as US2004/0087936 on May 6, 2004, application Ser. No. 10/754,452 of Jackson published as US2004/0215235 on Oct. 28, 2004, application Ser. No. 10/754,445 of Ganz published as US2004/0215296 on Oct. 28, 2004, application Ser. No. 11/244,385 of Jackson published as US2006/0095032 on May 4, 2006, and application Ser. No. 11/633,938 of Jackson published as US2007/0100333 on May 3, 2007) that make use of an expandable balloon to exert pressure from behind the ablational surface to press it against the target tissue area. Inasmuch as the inner diameter of luminal organs, such as gastrointestinal organs, vary in size, the extent or volume to which a balloon is inflated to achieve therapeutic contact will vary accordingly.
One currently available approach to creating consistency in the pressure that supports an appropriate or desirable level of therapeutic contact is to pre-test the target ablation site in order to know what inflated air volume is appropriate. Accordingly, measurements may be taken while pressurizing an oversized balloon to a specific pressure (for example, 4 psig) and then used to estimate the diameter of the esophagus, as described in U.S. patent application Ser. No. 11/244,385 of Jackson, published as US 2006/0095032. While this technique works well under ideal circumstances, in practical circumstances, leaks in the system can cause the production of inaccurate diameter estimates. Preventing leaks has been shown to be difficult as there are various locations in the system where a leak may occur.
Therefore, there is a need for alternative means of measuring the diameter or circumference of a body lumen in anticipation of a treatment, such as an ablation. This disclosure describes alternative devices and methods of accomplishing this task.